We are wanting to give a customized experience for customers that come to our clothing e-commerce store from different countries. When someone comes on our e-commerce store for the first time, we want them to see a pop-up from which they can select their country. On selecting their country, we want the currency of our website to change to their respective currency.

We use BigCommerce as our e-commerce platform and they have a neat feature where we can redirect customers to www.WEBSITE.com/?setCurrencyID=2 etc. to show visitors prices in their currency.

1.) Graphics of the pop-up will be provided by us. The pop-up should happen in the same window - maybe Javascript? Not the other annoying types.
2.) On selecting the country, the visitor should not get the pop-up for another 5 visits
3.) We want a custom drop-down list with the list of countries on the top of the pages so that if customer accidentally clicks on a country, he can switch